An underinflated tyre on a large jet is almost impossible to detect by eye and it is likely to creep so the marks might give you an early warning of a soft tyre.
Wheel braking during retraction serves a couple of functions. Firstly it stops any vibration as the gear goes into the well as this tends to scare the punters.
Most importantly if a tyre has failed on the takeoff roll it might well have long strips of tyre carcase spinning at high speed going into a wheel well lined with hydraulic reservoirs, valves, pipelines.
As a back up the Boeing 737 NG has small shear off fittings protruding below the wheel wells. If a spinning carcase hits one, it shears off dumping the hydraulic fluid from the gear retract line, the retract sequence stops keeping the damaged wheel out of the bay.
On the 737 there are no wheel doors and the wheels push up through rubberised blade seals. A spinning wheel would damage the seals as well as scaring the punters.
I believe that if you advance the throttles on a 737 with the parking brake set you trigger an audible configuration warning.
Last edited by ericferret; 21st Oct 2007 at 13:20.